The general objective of the proposed research is to understand how auditory information can be used to modify vocal output and thereby learn new vocalizations. Vocal learning has evolved independently in humans, songbirds and parrots, but has been studied extensively only in songbirds, where auditory responses can be recorded throughout most of the vocal motor system. In parrots, anatomical studies indicate that the vocal motor system receives inputs from auditory structures, but physiological recordings have thus far revealed no auditory responses within the vocal motor system. This discrepancy between the anatomical and physiological data suggests that in parrots auditory information may be gated out of the vocal motor system whenever vocal learning is not appropriate. If this hypothesis is correct, then manipulations of the putative gating pathway should facilitate the recording of auditory responses within the vocal motor system. Three specific experiments are proposed: 1. In order to confirm that auditory responses are indeed absent from the vocal motor system under normal conditions, complex auditory stimuli will be played to urethane anesthetized budgerigars, which are small parrots, while recording extracellular responses of neurons in both vocal motor and auditory structures. This experiment will provide baseline data for the second experiment. 2 In order to test the gating hypothesis directly, the putative gating pathway will be either inactivated or stimulated, depending on whether the gate is inhibitory or facilitatory in function. Inactivation will be accomplished by iontophoretic infusion of muscimol or lidocaine. Stimulation will be mediated by electrical pulses that are temporally correlated with the presentation of complex auditory stimuli. If the gating hypothesis Is correct, then one of these manipulations should facilitate the recording of auditory responses in the vocal motor system. 3 Bilateral excitotoxic lesions of the putative gating pathway will be used to assess its behavioral functions. According to the gating hypothesis, this manipulation should lead either to increased vocal plasticity or to a gradual deterioration of all learned vocalizations, depending on whether the gate is inhibitory or faciliatory, respectively.